As mobile telephone technology has advanced, the phone developers have concentrated on making the phone smaller so that more volume and weight could be set aside for battery storage, while keeping the overall form-factor of the phone to be pocket-sized. With the advent of new long-life battery storage technologies and low power digital modulation, the phone has been reduced to a size and battery life that is more than adequate in both departments. Now that these problems are effectively solved, an interest to adding new features to the phone beyond ordinary telecommunications has developed. Among these features is the accurate locating technology afforded by GPS receivers.
Adding a GPS receiver to a mobile phone permits dual use of many of the phone's current parts: embedded CPU, DSP, battery, user interface. Unfortunately, cellular downlink signals are different enough from GPS downlink that an entirely different antenna and filtering arrangement may be needed. For example, GPS downlink signals are typically circularly polarized, whereas cellular signals are not. Moreover, since dual antennas are needed, each antenna must be oriented so that while the mobile phone is positioned for each specialized use, as few phone parts and external obstacles are interposed between the external radio source and the phone antenna.
Since a mobile station such as a mobile phone must be highly miniaturized in order to provide its current functionality, designers adding new features must use as little real estate on the main circuit board as possible. Current generation circular polarized patch antennas, as described, for example, in the paper, "Compact Microstrip Antenna Loaded with Very High Permittivity Superstrate", Chih-Yu Huang and Jian-Yi Wu, IEEE Antennas and Propagation Society International Symposium 1998, Jun. 21-26 1998, Atlanta Ga., may occupy as little as a square 20 mm on a side. This type of antenna, and others that lack holes are continuous conductor type antennas. Because GPS depends on line-of-sight (LOS) operation between the satellite(s) and the receiver, the GPS receive antenna must be on the top of the mobile station while employed for its locating function--which means for purposes of human-readable output, the mobile station's display must be situated on the same side as the antenna. Furthermore, the GPS antenna must be on the distant end, as opposed to the end that is grasped. Moreover, on that same side, the antenna competes for space with display, keyboard, microphone and speaker as principal front-side mobile phone components.
Deploying the GPS antenna on a flip or a boom causes its own problems. A flip requires extra enclosing hardware, as well as a resilient path for conductors to carry signals between the flip and the main phone. More parts thus produce higher cost, greater weight, lower reliability among other problems. The same problems apply to any other component that is deployed on a flip or boom.